1. Field of the Invention
This invention relates to a light emission display drive method and drive apparatus preferred for use for multiple-level gradation display of a flat panel of organic EL, light emitting diode, plasma, etc.
2. Description of the Related Art
To change the light emission amount of each dot in the above-mentioned light emission display, the amount of charges injected within the drive time period of the target element may be changed and thus a method of changing the current value or a method of changing the on time with the current value fixed can be used.
For convenience, the former is called analog method and the latter is called pulse modulation or time division method. In the analog method, high-accuracy linearity is required to change the drive current in response to the brightness value; particularly, with TFT, the linearity and stability of the gate voltage vs drain current characteristic are poor and it is difficult to provide good performance.
On the other hand, in the pulse modulation method, a constant current needs only to be output and thus the drive section is miniaturized and the temperature characteristic is also good. In the pulse modulation, a 2n subframe method (weighting) is a method of separately controlling turning on/off eight subframes having drive times in the ratio of 1:2:4: . . . 128 based on the input value, thereby representing 256 gradation levels. A method of executing ΔΣ modulation in response to the input value for each pixel, controlling turning on/off based on the output, and controlling gradation based on the pulse density is also available.
However, in the pulse modulation, the former method has the disadvantage that if the weight ratio goes wide of the target, a rapid brightness level difference occurs in the high-order bit carry. For a moving image, a strong pseudo contour phenomenon still occurs in the high-order bit carry.
On the other hand, the latter method has the disadvantage that unless the oversampling ratio, namely, the number of subframes is raised to some extent or more, the on period per pixel at the low brightness time becomes drastically lower than the frame frequency, causing flicker to appear, degrading the display image quality.